Airplane wing or fin with improved airfoil characteristics



Patented May 28, 1946 UNITED ST AT IALIRPLANE TING on FIN wrrnmreiiovnn CHARACTERISTICS Vaile A. Cosier, :Wilmington, DeL, assigno r to E. .du Pont de Nemo ui-s & Company, Wilmington, Del., a corporation of Delaware No Drawing.-

; Application April s, 1942.

"Serial No.438,144 c pp a s s 2 Claims.

This invention relates to a process for finishing airplane wings and fins and more particularly to those with improved'airfoil surfaces.

In the construction of metal airplane wings and fins, customary procedure provides for the riveting of wing sections tosupporting structuresuIno'rder to reduce turbulence in the air flow passing overthe wing surface when the plane is in motion as caused bythe protruding rivet heads, the rivets are countersunk or laboriously filed off toproduce a smoothersurface.

Other surface irregularities also contribute to lowg-l er efiiciency of the airfoil 'with resultant loss in speed and'lift. It has beentestimated that if a;

perfectly smooth wing surface could be made avail-- able, the speed of a plane which normally may be operated at about 400 miles per hour could be increased asmuch as 40 miles perhour at maximum power output. Important fuel saving representsan additionalfactor. in approaching the objective of devising a means forg obtaining. Numerous a uniformlysmooth .wingsurface. methods for accomplishing the desired result, such as conventional. coating systems, havebeen proposed. but have been discarded because of failureto provide a uniformly smooth surface or because. ofw' excessive shrinkage, prohibitory weight increase or lack of sufiicient elasticity for:

irregularities in the winger fin surface; whichtissimple and practical in its operation.

Afurther object is the provision of a meansfor obtaininga uniformly smooth wing and fin surface which keeps added weight at aminimum. Otherfobjects will appear as the descriptionof the invention. proceeds.

These objects are accomplished by the appli cation toan airplane wing or finsection' of a potentially reactive organic polymer composi-- tion preferably comprising rubberfor a synthetic rubber polymer adapted to form a porous, sponge;

like structure andthereafter placing the coated unit in a, suitable mold and heatinguntil the.

composition has assumed a sponge-like structure and has become vulcanized or converted to a substantially inert state. s I In practicing the invention] in its preferred embodiment, the wing or fin surface is coated an adhesive adapted to adhere a subsequently applied rubber or synthetic rubber polymer compositionand allowed to dry. A rubber or synthetic rubber polymer. composition containing potentially gas-evolving chemical reactants is calendered onto afabric which may, if desired; also be presized with an adhesive of the above-mew.

tioned type. This composition is then placed on the adhesive-coated metal surface of the wing or fin with only moderate pressure which may. be done manually. with the fabric foundation exposed, The unit is then placed in a conforming mold, preferably oflight weight metalpwhich is oversize to permit expansion of :the modified rubber or equivalent polymer with the formation of a spongy structure upon heating. The .tem--.

perature of the c omposition is raised by anyt suitable means whereupon the gas-evolving chemical reactants incorporated in the rubber or.

equivalent polymer are caused to give off ages which imparts a porousstructure to the com- Partsby weight Crepe rubber (50 Mooney plasticityl n .360 Whiting 25 Zinc oxide- 3 Petrolatum 6 Stearic acid '5 Sodium bicarbonate '7 Antioxidant (phenyl beta-naphthylamin- 1 lfur 2 Accelerator (mercapto benzothiozol) 0.75.

position andat the same time expands the compositionto the opposite or interior surface of [the mold which thus provides a smooth continuous surface for the composition. During this treatment, the rubber or synthetic rubber polymer also becomes vulcanized or polymerized to inert state. Theflnal surface then is uniformly smooth over its entirearea, eliminatingall sur; face irregularities, and protuberances suchyas rivetheads.

The following examples are given by way for illustration only and-no limitations are intended thereby except as indicated in the appended claims. a :1 Example 1 A fabric sheeting weighingfabout i square yards per pound was base coated with aconventional rubber cement, commonly "consisting essentially of crepe rubberfrosin, reclaimed rub her and pitch dissolved or dispersed in gasoline,

or toluene. After the cement base coat-nae dried a rnodifiedfrubbercompound of the following composition was appliedto the fabrio at a thickness of 0.1 inch by calender application? fabric foundation was coated with a thin filmj pf therubber cement described above and allowed to pound on a supporting fabric base was applied manually over the entire surface of an airplane tail fin which was previously carefully cleaned.

to remove all dirt and grease andcoated with a thin film of rubber cement, with the rubber sur-" face next to the adhesive coated metal fin surface taking care that the abutted edges of any cut-out sections of the composite sheeting were in close contact to insure complete continuity in the final surface covering. U. 18. Royal cement was found to be particularly suited for use in Joining the rubber compound to the metal fin surface.-

The tail fin carryingthe rubber coating in an intermediate stage. with the fabric support outer-J most was placed in a light weight metal .conforming mold loosely fitting to theextent that an expansion-of the rubber compound covering to. about 0.25 inch was allowed. The mold :was-

heated by steam to a temperature of320 F..-for a period of /2' hour. compound expanded to a thicknessup to about During this treatment the 2,400,918 dry. This sheet consisting ofthe rubber comtime the neoprene compound expanded to a thick- 0.25 inch and assumed a spongedike, porous.

structure caused by the evolutionof gaswithin the rubber compound. At the same time the rubber wasvulcanized to impart characteristic 'resilient properties to the rubber compound. "Theresulting covering had "a uniformly continuous,

smooth surface covering the irregularities in the metalfin'surface, including rivet heads which to the interior of the mold, satisfactory results are so largely responsible for the loss in operating emciency of an airplane.

Example? v Parts by weight Neoprene I 60, Pine tar I 2 Woodrosin 7 j '3 Calcined magnesia Sulfur .11, Zinc oxide 7 i g I 6 Whiting 22 The above composition was dispersed'in toluol and spread on the fabric with a conventional doctor'knife so as to deposit 1 ounce per yard of solids after evaporating the solvent.

0.1 inch of the following composition was then applied by calender application to the cement.

coated side of the fabric:

The surface of the wing was cleaned and Painted with a thin film of a rubber cement consisting of a gasoline dispersion of rubber, rosin, reclaimed rubber. and pitchand allowed todry. q

The above neoprene coated fabric was then applied manually over th entire surface of the ness of approximately 0.25 inch and assumed a sponge-like structure. due to the evolution of gas within the compound. Atrthe same time the compound was-vulcanized or polymerized to a permanent resilient form. i

The resultant product was characterized by a uniformly continuous smooth surface covering the irregularities in the wing surface, including the rivet heads. I

Althoughin the example, heating of the rubber compound is accomplished by supplying steam mayalsobe secured by supplying steam .directly to the interior of the wing or finstructure. Suite able electric heating means may also be employed ifdesired.- a v.

- I have found that-for. practical operation of the present'proeess in casesin which large surface areas are. involved and in which these surr faces have a curving contour, the use of a fabric A cotton sheeting weighing about 4 square. yards per pound was base coated with a neoprene cement of the following composition:

. ofequivalent fibrouarporous material is -essen-.

tial over the surface of the potentiallysponging rubber or synthetic rubber polymer. This modification eliminates pits. and indentation imperfections'caused by entrapped air or gas by allowing it to escape. from the mold: cavity through the fabric and thus provide a .more' uniformly smooth surface for the wing'or fin covering. The use of the fabric also preventsthe sponge rubber from sticking to the'mold and facilitates shipping and' tailoring. of i the unvulcanized sponge rubber composition. It also provides a base for the application of surface coatings to which good adhesion can be obtained. Desirable surface d. coatings consist of durabldpfiexible materials which may" contain cellulose derivatives, syn thetic resins, oleoresinous compositions, synthetic or natural rubber polymers and which may be applied-as a. solution in-volatile solvents or in the form of a latex, or similar materials. They should be-preferably applied fromsolutions, the viscosity of which is such that on application the fine imperfections of the fabric are filled and the coating levels into a smooth surface but mateposed for long periods to temperaturesi'as low as -25 F. or even 40 F., itv shouldnot become brittle or subject to fracture. On the other hand the coating must be resistant to-sunlight and high temperatures as would be found in'the tropics whichmay reach as much as F. or more-on the surface without displaying serious change of properties. The coating must also be resistant to rain, snow, and abrasion such as produced by ordinary impacts of tools or pebbles and by workmen-walking on the wings. When synthetic or natural rubber polymers in the form of solutions in volatlleliquids or latex are applied, they maybe of the air curing type or of those. which require the application of .heat for vulcanizae,

tion. Inthe latter case, the entire wing may be placed in a full or sectional mold having a polished contact surface so thatafter vulcanization ,has taken place, the finished winghas a smooth glossy surface. If necessary, "stickingto the, mold may be prevented by any suitable meansknown in the art, such as by; the use of; dusting powder, mold solutions, etc.

-According to thepresent inventiomthe unvulcanized natural or artificial sponge rubber example is not strictly limitative since thethicknessjmay bevaried considerably 130 meet specific requirements. "In anyevent; itis essential that the ultimatejcoating thickness be greater than surface, irregularity including protruding rivet heads. Excessive coating thickness should generally be avoided since no advantages accrue thereby and the unnecessarily increased weight compound may be applied directly toa suitable fabric by calendering. Usually the potentially spongy composition is secured to the fabric by means of a thin layer of rubber or neoprene cement which may be applied tothe fabric before calendaring thereon the sponge layer. After,

prene or other synthetic rubber polymer which may or may not be already vulcanized or polymerized as desired, previously coated with a rubber adhesive and dried, applied over the surface a of unspongedrubber followed by blowing this assembly as previously described. This provides an unusually smooth surface and also effectively seals any pores which might be present as a result of the sponging treatment. The skin film is tightly adherent since it becomesfvulcanized into the spongy base during the heat treatment.

since this material affords grease and oil resistance and greater general durability on outdoor exposure. Thin metallic foil may also be employed in covering the sp ngerubber or synthetic rubber polymer. A final top coat finish of conventional type as previously described may be applied if desired.

The hardness of the covering may be varied considerably to meet special requirements by varying the composition to control the degree and contributes to counteract the improvements accomplislied by theiinvention when it is properly practiced. A thickness of coating up 'toabout 0.25 inch is ordinarily suihcient.

The requirements for-adhesion ofthe coating to the metal wing orfinsurfaces are norminal. u

It is estimated,thatthere is asuction force on top of the airplane wing of seldom more than 4 pounds per square inch so" that theadhesive strength of the bond between the metal surface of the wing and the coating compound need only be on that order. I The ordinary rubber cements, howevens'uch' as that suggested in the examples afford Joint stren'gthsin excess of therequirement just noted so that acceptable adhesion between the metal, surface of the wing or fin is readily obtained inoperating the process of the inven-. tionQ Light sand-blasting. of ,themetal surfaces may also be employedindeveloping agood bond. Adhesion in some cases may also be improved by suitable pro-treatment of the metal wing orfin surface such as byplating the surface with nickel The skin film preferably consists of neoprene salts. u u

While in the examples the porous spongy structure was developed in the rubber compound coating by the evolution of gas from reacting chemicals, similar results may be obtained by pumping a foamed rubber latex or synthetic rubber soluor copper or by known treatments with metallic it tion into a loosely fitting mold containing the wing or fin and applying heat to vulcanize the j plastic in the presence of trapped-air bubbles.

The primary advantage of the invention, is the elimination or marked reduction in wing drag from turbulence in air flow over thewingsurface heretofore encountered because of surface irregularities and protuberances such as rivet heads. This improvement affords significant advantages in performance and operating efficiency, particularly as regards speedincreases of important magnitude and in fuel economy. The improved wing and fin structures do not add excescharacter of sponging. by varying the milling.

composition and by confining the composition in a closer fitting mold during the heat treat- I ment.

Instead of the rubber compound shown inExample 1, other rubber compounds of equivalent chemical and physical properties may be employed. Synthetic rubberpolymer, for example,

neoprene, such as described in U. S. Patent 1,950,431 and manufactured by E. I. du Pont de cycle of the crepe rubber used in preparing the sive weight to the airplane unit, afactorwhich g is obviously important for either military or commercial aircraft. The wing or finsurface as afforded in the practice of the invention which is l uniformly smooth over the entire surface area is also characterized by the ability of withstanding great temperature extremes which, in ex-- treme cases, may range from F.to 150 F. for the airplane in service. A further important advantage resides intlie greatresiliency and elasticity of the coatingwhich withstands continued Nemours 8: Company, essentially a plastic polymer of 2 chloro-butadiene 1,3; 'I'hiokol, an ole- I fine polysulflde resin; Bllna rubber, a synthetic polymer consisting essentially of butadiene; or

other synthetic rubber polymer of equivalent properties are also satisfactory.

The coating maybe applied over the entire wing or fin structure and overpart or all of the aircraft fuselage if desired, although in some instances it may suffice to coat only the forepart of the wing, for example; theforemost one-- third part of the wing where uniform smoothness to avoid air turbulence ismost important.

vibration and wing deformations amounting to deflections of as much as 2 feet up and 1 foot down sometimes encountered during flight. This property of'great elasticity is of considerable benefit also because of the very great difference in the coefficient of expansion between the metal structure of thewing or fin and the coating since the adhesion strength between these entirely unrelated materials is not impaired as would be the casein coating compositions where'high elasticity islacking. v

Conventional rubber coatings of non-spongy character applied to certainportions of airplane The thickness of the coating indicated in the surfaces by orthodox methods have been employed for tie-icing purposes, but such coatings and processes are in no sense to be considered the equivalent of the present invention; Coatings of this nature for the present purpose would involve intolerable excessiveadded weight and in order to mold them to the wing or fin surface to smooth out all surface ir'"egularities, heavy and expensive molds, and high pressures such as would distort the wing or fin structures would be required thus rendering such systems incapable of attaining the aforementionedobjectives. I

It is apparent that many widely different embodiments of this invention maybe made .without departing from the spirit and scope thereof, and therefore, it is not intended to be limited except as indicated in the appended claims.

ing, tailoring the said coated fabric over the said airplane part coated with the bonding cement, the sponge rubber layer being in contact with the cement on the said metal body, placing the coated airplane part in a mold slightly larger than the coatedpart, heating'to cause the rubher to expand and fill the mold and having the rivet heads embedded therein without causing protuberances on the surface and thereafter applying a film of a flexible weather resistant material over the'said fabric.

2. The process of claim l'in which the sponge rubber layerhas approximately the following composition:

' Parts by weight Crepe rubber Mooney plasticity) Whiting 25 Zinc oxide 3 Petrolatum; 6 Stearic acid; 5 Sodium bicarbonate 7 Anti-oxidant ('phenyl beta-naphthylamine) r i Sulfur 2 Accelerator (mercapto benzothiozol) 0.75

Diphenyl guanidine 0.15

VAILE A. COSLER. 

